The present invention relates to an apparatus and method for encoding images, and also to a decoding apparatus and method for decoding coded data.
Hitherto, television signals have been encoded by using data about the surrounding of the pixels to be transmitted. This is because an image generally exhibits acute auto correlation with a neighboring region. Thus, the data about the neighboring region should be used to compress data efficiently.
From a microscopic point of view, however, any correlation cannot be said to exist at an edge part of an image, where the signal greatly change, whereas the correlation is strong at a flat part where the signal does not change.
In such a case, that part where the correlation is strong is encoded by fully using the strong correlation, while the edge part is encoded by applying a suitable amount of data or is encoded within a scope where visual masking effect can be obtained.
In the conventional encoding method described above, an image is encoded by applying an appropriate amount of data for an edge part of an image. There is inevitably a limit to the reduction of data. That is, the encoding efficiency is low.
The present invention has been made in view of the foregoing. An object of the invention is to provide an encoding apparatus and method which can reduce an amount of data even at an edge part and which can encode signal values with high efficiency.
Another object of the present invention is to provide a decoding apparatus and method which can easily decode an image encoded in accordance with its characteristics and then transmitted.
Accordingly, an encoding apparatus according to the present invention is characterized by comprising: a data-grouping section for dividing a plurality of pixel data items of an image signal, into groups, in accordance with characteristics of the image signal; and an encoding section for encoding the pixel data items of each groups on the basis of level data representing a signal level of a representative pixel data item of the group and position data concerning all pixel data of the group.
A decoding apparatus according to the invention is designed to decode a plurality of pixel data items having a specific order from a plurality of coded pixel data items which have been generated by dividing image signals, each composed of pixel data items having the specific order into a plurality of groups in accordance with characteristics of the image signals and by encoding the pixel data items of each group on the basis of level data representing a signal level of a representative pixel data of the group and position data concerning all pixel data items of the group. The decoding apparatus is characterized by comprising: a level-data extracting section for extracting the level data from the coded pixel data items of each group; a position-data extracting section for extracting plurality of position data items from the coded pixel data items of each group; and a data-converting section for converting the pixel data items of each group to ones arranged in the specific order, on the basis of the level data extracted by the level-data extracting section and the plurality of position data items extracted by the position-data extracting section.
An encoding method according to the present invention is characterized by comprising: a step of dividing a plurality of pixel data items of an image signal, into groups, in accordance with characteristics of the image signal; and a step of encoding the pixel data items of each groups on the basis of level data representing a signal level of a representative pixel data item of the group and position data concerning all pixel data of the group.
A decoding method according to the invention is designed to decode a plurality of pixel data items having a specific order from a plurality of coded pixel data items which have been generated by dividing image signals, each composed of pixel data items having the specific order into a plurality of groups in accordance with characteristics of the image signals and by encoding the pixel data items of each group on the basis of level data representing a signal level of a representative pixel data of the group and position data concerning all pixel data items of the group. The decoding method is characterized by comprising: a step of extracting the level data from the coded pixel data items of each group; a step of extracting plurality of position data items from the coded pixel data items of each group; and a step of converting the pixel data items of each group to ones arranged in the specific order, on the basis of the level data thus extracted and the plurality of position data items thus extracted.